Dedicated devices for accessing digital data services such as Internet Protocol Set Top Boxes for rendering of audiovisual services (e.g. IPTV-STBs) have minimal hardware resources in order to reduce production costs and ensure a competitive market price. In particular, processing and memory resources are tailored to the strictly needed. But with ever enhanced service offers and improved graphical service offering presentation, service portals, that are the entry point to access a service offering, become more and more complex and demanding with relation to the limited resources of the dedicated devices. Service portals typically comprise a hierarchy of menus and pages, comprising not only text, but also voluminous images and scripts that must be executed. All of this information must be downloaded from a remote server in a network before being rendered, which slows down the reaction time of the devices. Important processing and memory resources are required, in order to ensure sufficient reactivity of the devices for users, which conflicts with a requirement to keep the production costs of the devices low. According to prior art solutions, local cache memory is used to speed up the rendering of menus and pages, so that information that is needed and that has already been downloaded once is fetched from local cache memory instead of being downloaded each time it is needed. But ever increasing enhancement of service offering results in very quickly filling of cache memory when a user navigates among the pages of a service offering access portal. Working with a completely filled cache that is managed according to prior art cache management is problematic because it introduces undesirable delays; each time new data is to added to a full cache, a so-called ‘best candidate’ must be found to be removed from cache, that does not penalize the reactivity of the device too much. Prior art solutions try to optimize this search for a ‘best candidate’ by applying different cache management policies related to time stamping of the last use of data stored in cache, and removing relatively ‘old’ information from cache. But cache management also introduces delays. In some situations, the delay needed for the cache management is higher than the delay that is caused by direct downloading of the required data from the network; a situation which is difficult to evaluate beforehand. In addition, the ‘best candidate’ chosen according to a specific cache management policy is not always the best choice; for example, it is not desirable to remove from cache memory the pages and resources of a main service offering access portal application that functions as an entry point for a user to access a service offer, even if the data related to that main service offering access portal is the ‘oldest’ data in cache.
There is thus a need for an optimized cache memory management method where delays introduced by management of full cache memory are avoided and removal from cache memory of important information is avoided.